1. Field of the Invention
This invention relates to planar lightguide circuits, in particular those employed in multiplexing and demultiplexing of signals
2. Discussion of the Related Art
Dense Wavelength Division Multiplexing (DWDM) is the terminology applied to the latest efforts to improve the effectiveness of optical signal multiplexing and demultiplexing. DWDM, particularly that provided on a Planar Lightguide Circuit (PLC), is very attractive for mass-production of passive components for optical fiber communication systems.
Presently, many attempts are being made to use UV laser-induced fiber gratings in sensitized optical fibers to produce wavelength-selective passive components. Nevertheless, to use such gratings, one must either use a 3 dB splitter-combiner to handle the selected and back-reflected wavelength, and thereby incur the disadvantage of a 6 dB minimum insertion loss, or use a circulator, which is complex, expensive, and bulky. It is desirable to avoid these disadvantages.